Thomas a



(No Model.)

T'. A. EDISON. MANUFACTURE OF CARBON PILAMBNTS.

No. 438,299. Patented Oct. 14, 1890.

ATTEBT! i INVENTOR: 6% 7/ V @1441 UNITED STATES FFICE.

ATENT THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY, ASSIGNOR TO THE EDISON ELECTRIC LIGHT COMPANY, OF NEW YORK, N. Y.

MANUFACTURE OF CARBON FILAMENTS.

SPECIFICATION forming part of Letters Patent No. 438,299, dated October 14, 1890.

Application filed March 16, 1883. Serial No. 88,353. (No model.)

To aZZ whom it may concern.-

Be it known that I, THoMAs A. EDISON, of Menlo Park, in the county of Middlesex and State of New Jersey, have invented a new and useful Improvement in Carbonizing, (Case No. 541,) of which the following is a specification.

My invention relates to the process of carbonizing filaments for the incandescing conductors of electric lamps. I have found that the higher the temperature to which such filaments are raised before decomposition commences the more complete will be the carbonization and the more compact and homo geneous will be the residual carbon remaining after the process. By placing the filaments during carbonization under a higher than atmospheric pressure the temperature necessary for decomposition is raised to a point higher than the normal one. To accomplish this result, I place the filaments in a closed flask, in which is placed a quantity of hydrocarbon or of any other substance, which when heated gives off a gas or vapor other than oxygen-that is, one which will not injure the filaments during carbonization. The gas or vapor given off by this substance increases the pressure in the flask to the desired point. In order to maintain this increased pressure, I place the flask within an outer closed flask or chamber, which also contains a quantity of the same or asimilar substance, and the gas or vapor given off by which prevents a reduction of pressure by leakage from the inner chamber.

My invention is illustrated in the accompanying drawing, which is a sectional view of the apparatus employed.

A is an outer flask, and B an inner one, both being made of a materialsuch as carbon or nickel-capable of withstanding high temperature. Each is provided with a tightlysecured cover. Within the inner flask B are placed the molds a a, containing the filaments to be carbonized. The whole is placed in a suitable furnace, the outer flask A being of such height that its upper part projects well above the fire.

Within each flask is placed a portion of the hydrocarbon or other compound I"), which upon composed. After carbonization the cover of the flask A is removed and the chamber B can then be lifted out.

\Vhat I claim is 1. The method of carbonizing, consisting in heating the carbonizable material in the 6;

presence of a substance which gives off a gas other than oxygen to increase the pressure in the carbonizing-flask, and maintaining such pressure by heating a similar material in a chamber surroundingsaid flask, substantially as set forth.

2. The combination, in carbonizing apparatus, of a flask containing the material to be carbonized and a substance which gives off a gas other than oxygen when heated, and an outer inclosing-flask containing a similar substance, substantially as set forth.

3. The combination, in carbonizing apparatus, of a flask, a series of molds in said flask containing the material to be carbonized, a substance in said flask which gives off a gas other than oxygen when heated, and an outer inclosin gflask containing a similar substance, substantially as set forth.

This specification signed and witnessed this 17th day of February, 1883.

THOS. A. EDISON. Witnesses:

H. WV. SEELY, EDWARD H. PYATT.

The press- 55 

